Heretofore, a type of a seated passenger's weight detection device which is applied to a seat slidably disposed in the vertical direction on a floor of a vehicle of an automobile and so on is disclosed in Japanese Patent Laid-Open Publication No. 11-304579. As shown in FIG. 6, this seated passenger's weight detection device is provided with a seat connecting mechanism 206 which connects between a seat bracket 200 of the vehicle and a seat 202 and which includes an arm 204 being rotatable upward and downward and a load sensor 208 between the seat 202 and the vehicle. Further, the arm 204 is pivoted on a rotation fulcrum 210 of seat side and a rotation fulcrum 212 of vehicle body side and the load sensor 208 receives selectively a vertical direction component of a weight of the seat operated to the arm 204.
In this seated passenger's weight detection device, however, as shown in FIG. 7, in case that a seat vertical position adjusting means 222 being able to adjust a position in the vertical direction is disposed on the seat 202, a seat cushion flame 228 and sensor brackets 232 fixed on an upper slide rail 230 are connected by a front link 224 and a rear link 226 constituting the seat vertical position adjusting means 222 and axis 240, 242.
Hereby, a downward component force F2 and a forward component force F3 of an input F1 from the front link 224 operate to the sensor bracket 232 of front side through the axis 240 by an angle α of inclination of the front link 224. Thereby, a downward input F4 from the rear link 226 connected to an actuator 244 of the seat vertical position adjusting means 222 and a reaction force F5 of the component force F3 operate to the sensor bracket 232 of rear side through the axis 242. Namely, extra forward force F3 or extra backward force F5 other than the downward forces F2, F4 being required for strain sensors 246 as the load sensors disposed on the sensor brackets 232 operates to the sensor brackets 232. These forces F3 and F5 are applied as tension and compression forces directly to the sensor brackets 232 on which the strain sensors 246 are fixed. Therefore, the forces F3 and F5 make the stain sensors 246 generate unnecessary strain and there is in danger that the measurement accuracy of the load operated to the seat decreases.